Chapter 26, Problem 12STP

Summary Introduction

To analyze:

The development of zygote in different stages.

Introduction :

Different animals have different features in their feeding process, development of their body, and the features that involve as their support in the body structure. Some of the animals are invertebrates and it involves all the animals that have exoskeletons. The exoskeleton is the outer coverage of the body, it is the tough or hard outer cover, it provides support to the soft tissue of the body, avoid loss of water, and also give the protection of the predators. The endoskeleton is the internal covering of some of the vertebrates. It involves sea stars and sea urchins; they are made of calcium carbonate, cartilage, etc. Unlike different cell structure different animals have different reproductive structure. One of the features includes hermaphrodites, the animals that produce both sperms and egg. They produce egg and sperm simultaneously with the help of sexual reproduction. They undergo embryo development through mitotic cell division. Some of the organism also undergoes asexual reproduction through the process of regeneration and some are parthenogenesis, form zygote without fertilization of eggs.

Explanation of Solution

The animals that produce both sperms and egg are considered as hermaphrodites. When the sperm get ejaculated inside the female body, the egg gets fertilized to form zygote. The zygote then undergoes mitotic cell division and form two cells that are termed as embryo. The embryo undergoes continued division and form 16 cell stage, that is the blastula stage. In the early stage the number of cell get increases but the cytoplasmic amount remains same as in the initial stage of division. Because of this the size of embryo remains constant in the early development. Gastrula is a two layer sac with an opening at one end formed in embryonic development. In some animals the zygote undergoes mitotic cell division and form two cells that are termed as embryo. The continued division of embryonic cell form blastula. Animals like frogs undergo further division of cell to form gastrula. It seems like a double bubble that means one bubble inside another bubble.

Conclusion

The zygote thus form from the fertilization undergoes mitotic division and form embryo and the further division form blastula and the gastrula.